This invention pertains to the use of on-board gasoline partial oxidation systems on automotive vehicles. More specifically, this invention pertains to methods and apparatus for storing and using fuel vapor for cold starting a partial oxidation reactor of an internal combustion engine-powered vehicle or a fuel cell-powered vehicle.
Automobile manufacturers continue to develop methods and apparatus for reducing the exhaust emissions of cars and trucks. One avenue of development is the use of hydrogen-containing fuels in both internal combustion engines and fuel cells. Hydrogen burns cleaner and in more fuel lean mixtures with air than gasoline. Since hydrogen is difficult to store and carry on the automobile, practices are being developed to make hydrogen on-board the vehicle by the partial oxidation of gasoline hydrocarbons to reform them as hydrogen and carbon monoxide. Carbon monoxide is usually removed by a separate processor for fuel cell applications.
Thus, on-board gasoline partial oxidation (POx) reforming is one of the technologies being considered for very low emission vehicles. A POx reformer combines gasoline and air under very fuel-rich conditions to produce hydrogen-rich POx gas as shown below:
C8H18+19 Air (4O2+15N2)=9H2+8CO+15N2+Heat
It is known that adding hydrogen to gasoline allows a spark ignition, internal combustion engine to run very lean due to hydrogen""s wide flammability limit. Leaner mixtures provide relatively low combustion temperatures, which lower engine out NOx. Gasoline can be carried on the vehicle in a conventional fuel tank and pumped from the tank in separate streams to the fuel injection system of the engine and to a POx reactor. The output of the POx reactor is also added in controlled amounts to the fuel induction system of the engine for mixing with gasoline vapor and air in the combustion chamber of the engine. The POx reactor can also be used when the vehicle is powered using a fuel cell of the type in which hydrogen is reacted electrochemically with oxygen for electric power generation in the vehicle.
Even with the advent of partial or total fueling of a vehicle using gasoline and a POx reactor, there remains the problem of cold start of the POx reactor and the engine or fuel cell. It is an object of this invention to provide methods and apparatus for the cold starting of a rector utilized on a car or truck for the partial oxidation of gasoline and the reforming of gasoline to a hydrogen containing fuel.
This invention is applicable on vehicles that store liquid gasoline in a fuel tank for delivery to an internal combustion engine and/or a fuel cell for producing motive power for the vehicle.
In the case of the gasoline-powered engine, the fuel storage and delivery system usually comprises a fuel tank, often at the rear of the vehicle, and a fuel line through which liquid gasoline is pumped to the fuel induction system of the vehicle""s spark ignition engine. The fuel induction system, in turn, comprises a fuel rail supplying a solenoid-actuated fuel injector for each cylinder of the engine. As is known, the timing and duration of activation of the respective fuel injectors is managed by a suitable engine control module comprising sensors and a suitably-programmed computer. When POx fuel is used in combination with gasoline, a separate fuel line supplies gasoline to the POx reactor and a line from the reactor supplies the hydrogen-containing fuel to a separate engine fuel injection system which is also under the control of the engine control module.
In the case of the fuel cell power system, the fuel storage and delivery system also comprises a gasoline fuel tank and fuel line through which gasoline is pumped to the POx reactor. The hydrogen-containing fuel from the reactor is further processed, if necessary, to remove carbon monoxide and then conducted to the fuel cell. Again, the delivery of gasoline to the reactor and the delivery of POx fuel to the cell(s) is usually controlled by a control system of sensors and a suitably programmed computer responsive to the power demands of the vehicle on the fuel cell. As is known, the electrical power output of the cell is used to drive the vehicle""s electric motor(s) or stored in a storage battery.
The on-board vehicle fuel tank for either the engine or fuel cell will usually be provided with a fuel evaporation control system to collect fuel vapor produced during tank refills or fuel evaporated at other times. The vehicle fuel tank experiences ambient temperature changes and other fuel heating events that cause fuel evaporation. Since fuel tanks are not intended to contain gasoline under high pressure, they are normally vented to a suitable fuel evaporation control (EVAP) canister containing activated carbon granules that adsorb and temporarily store evaporated fuel vapor. It is temporarily stored, gasoline vapor that is used in accordance with this invention to facilitate the cold start of the vehicle""s POx reactor. The practice of this invention is useful whether the hydrogen-containing product of the reactor is fed to an engine or fuel cell.
In accordance with the invention, the vehicle""s fuel tank is vented first and directly to a suitable POx vapor accumulator canister. The canister may be a cylindrical, molded thermoplastic container provided with a vapor inlet and a vapor purge outlet and a vapor vent outlet/purge air inlet. The canister is filled with a bed of particles of a suitable fuel adsorption media such as activated carbon. The design of the POx vapor accumulator canister is preferably such that vapor enters at the vapor inlet and must traverse the whole bed of adsorbent carbon before exiting the vent outlet. The vapor purge outlet is located at the vapor inlet end of the vapor flow path through the bed. And the purge outlet is connected through a suitable vapor duct to the inlet of the POx reactor. The vent outlet, which may exhaust to the atmosphere, is preferably connected to the vapor inlet of a suitable familiar (EVAP) canister. Thus, overflow from the POx vapor accumulator canister is stored in an EVAP canister which is purged directly to the engine fuel system intake as permitted by the engine control computer during engine operation in the known manner.
When engine or fuel cell cold start is to occur, stored fuel vapor from the POx vapor accumulator canister is drawn through the purge vent and duct from the adsorbent bed with reverse air flow through the overflow vent by operation of the engine POx fuel delivery system to the inlet of the POx reactor. The fuel vapor purged from the POx accumulator canister is typically rich in butanes and pentanes which are particularly suitable for POx reactor cold start. In a preferred embodiment of the invention, the C4-C5 mixture with air flows past an oxygen sensor, or the like, to estimate the air-to-fuel mass ratio (A/F) in the purge stream. Additional ambient air is drawn into the purge line upstream of the cold POx reactor to provide a suitable A/F (e.g., about 15) for combustion at the reactor inlet.
At the inlet of the cold POx reactor, the air-purged fuel mixture is ignited using any suitable means. For example, a glow plug or a spark plug may be activated at the reactor entrance to ignite the combustible mixture. The POx reactor may be of known design for such purpose. In other words, the reactor is of flow-through design in which the flow passages utilize a surface catalyst to promote the partial oxidation reaction. The burning of the ignited combustible mixture heats the catalyzed surfaces in a period of a few seconds or so to a suitable temperature for continued operation. For example, the burning of the combustible air-fuel mixture may be employed to heat the POx reactor to an operating temperature of 800xc2x0 C. or so, and then the fuel supply switched to liquid gasoline at a suitable A/F for POx reaction. In another mode of operation, the combustible purged vapor air mixture is used to heat the POx reactor to a light off temperature of 400xc2x0 C. and then the A/F of the mixture reduced to about 5 to generate POx gas in the reactor to continue heat up to 800xc2x0 C. and for POx fuel for engine cold start.
Thus, the use of a POx reactor vapor accumulator canister and purge vent in combination with the fuel tank and POx reactor for either an engine or fuel cell permits the use of specially stored and purged fuel vapor in the start up of a cold (ambient temperature) POx reactor. The quick heat-up of the reactor using stored evaporative fuel permits the faster introduction of POx fuel into the cold engine and/or fuel cell during start-up to reduce exhaust emissions and increase efficiency of the motive power source. While the cold engine may be rapidly started on 100% gasoline in accordance with known practices, the rapid start-up of the POx reactor using this invention permits faster operation in the fuel-lean mode obtained only by POx fuel addition and the resulting improvements in efficiency and emissions reduction.
Other objects and advantages of the invention will become more apparent from a detailed description of the invention which follows.